This invention relates to water swellable absorbent articles made from crosslinked polyelectrolytes, methods for their preparation, and to an aqueous solution consisting of polyelectrolytes containing free carboxylic groups which is useful to make absorbent articles.
It is known from U.S. Pat. Nos. 3,669,103 and 3,670,731 that cross-linked polymeric sorbents can be sandwiched between flexible supports to achieve disposable diapers or dressings.
It is further known from U.S. Pat. Nos. 2,988,539; 3,393,168; 3,514,419 and 3,557,067 that water swellable cross-linked carboxylic copolymers can be prepared. However, these prior art copolymers are all crosslinked during copolymerization or crosslinked after polymerization with subsequent neutralization of the carboxylic acid groups to form water swellable polyelectrolytes and hence these prior art polyelectrolytes cannot be crosslinked in situ as a coating on a substrate or as a flexible film thereof.
It is further known from Ser. No. 468,794, filed May 9, 1974 that carboxylic synthetic polyelectrolytes can be crosslinked after polymerization by the use of a nucleophilic displacement reaction using polyhaloalkanols, sulfonium zwitterions, haloepoxy alkanes, polyglycidyl ethers and mixtures thereof. These crosslinkers are active over a pH range from acidic to basic and must therefore be shipped separately and added to the polyelectrolyte solution at the point of use rather than the point of manufacture. The advantage of the present invention is that the crosslinking reaction proceeds only under acidic conditions and the user need only acidify the pre-mixed polyelectrolyte and crosslinker to achieve a crosslinkable composition useful in fabricating absorbent articles. The acidification is much less critical than adding the exact amount of crosslinker so the chance of error spoiling a batch is minimized for the user.